In portable communication devices, such as mobile phones, there is normally provided a built-in speaker for conveying sound (such as sound reproducing speech from another party in a voice-call session) to the user's ear in a so called “handset mode” (i.e. when no handsfree or headset unit is used). The speaker is adapted to be held to the user's ear in the handset mode, such that the sound generated by the speaker is adequately transferred thereto.
For a mobile phone in the handset mode, the sound characteristic in the receiving direction (i.e. as heard by the user's ear) changes with position and application force to the user's ear due to a varying leakage of sound. Normally, the more the leakage, the less low frequencies are heard. An ear speaker system can be designed to have more or less difference in sound characteristic between different amounts of leakage, which is referred to as various degrees of leak tolerance. With a low leak tolerance, the variation in sound characteristic with varying leakage is high, and vice versa.
The leak tolerance can be improved by various acoustical/mechanical design methods. However, such design methods require relatively powerful, and thus large, transducers. This is a disadvantage e.g. in terms of size, weight, and/or power consumption for the mobile phone.
One solution for leak compensation based on the electrical impedance of the speaker is disclosed in EP 1 523 218 A1.